The present invention relates to a seat belt retractor installed in a vehicle such as an automobile for retracting and withdrawing a seat belt. More specifically, the present invention relates to a seat belt retractor with an energy absorption mechanism (hereafter referred to as EA mechanism) for absorbing energy applied to a passenger moving due to inertia. The energy is absorbed by the seat belt when withdrawal of the seat belt is prevented in an emergency situation such as a crash when a large deceleration force is applied on a vehicle while the passenger is wearing the seat belt.
A conventional seat belt apparatus installed in a vehicle such as an automobile comprises a seat belt retractor for retracting a seat belt, a seat belt retractable from the seat belt retractor and having an end fixed to a vehicle body, a buckle fixed to the vehicle body, and a tongue for slidably inserting the seat belt and engaging the buckle.
When the passenger is not wearing the seat belt, the seat belt is wound on a spool of the seat belt retractor. After the passenger is seated in a vehicle seat, the passenger wears the seat belt by withdrawing a predetermined length of the seat belt from the seat belt retractor and inserting the tongue into the buckle. When the passenger is wearing the seat belt, the seat belt extending from the tongue to the seat belt retractor functions as a shoulder belt passing over a shoulder to a chest of the passenger. The seat belt extending from the tongue to the connection with the vehicle functions as a lap belt passing around the passenger hip.
When the passenger is wearing the seat belt, the seat belt is prevented from being withdrawn in an emergency situation when a lock mechanism of the seat belt retractor is activated to stop the rotation of the spool in the seat belt withdrawal direction. The shoulder belt of the seat belt apparatus restrains the shoulder and the chest of the passenger, and the lap belt restrains the passenger hip. In this way, the passenger is protected from being thrown off the seat.
Such a seat belt retractor in the conventional seat belt apparatus has the seat belt for restraining and protecting the passenger in an emergency situation such as a crash. During a crash, the vehicle decelerates rapidly, and due to the large inertia, the passenger moves forward. Therefore, large load is applied to the seat belt due to kinetic energy of the passenger.
The seat belt retractor in the conventional seat belt apparatus has a torsion bar for absorbing the kinetic energy applied in the emergency situation when the passenger is wearing the seat belt. As a result, the load applied to the seat belt is reduced.
FIG. 5 is a sectional view of a seat belt retractor having such a torsion bar. In FIG. 5, reference numeral 1 indicates a seat belt retractor; reference numeral 2 indicates a U-shaped frame; reference numeral 3 indicates a seat belt; reference numeral 4 indicates a spool rotatably disposed between sidewalls of the U-shaped frame 2 for retracting the seat belt 3; reference numeral 5 indicates a deceleration sensing mechanism for sensing rapid deceleration of a vehicle in an emergency situation; reference numeral 6 indicates a lock mechanism to be activated in response to the deceleration sensing mechanism 5 to prevent the spool 4 from rotating in the seat belt withdrawal direction; reference numeral 7 indicates a torsion bar loosely passing through the center of the spool 4 in the axial direction and connecting the spool 4 and the lock mechanism 6; reference numeral 8 indicates a spring mechanism for constantly urging the spool 4 in the seat belt retraction direction with a bush 10 by the spring force of a spiral spring 9; reference numeral 11 indicates a pretensioner to be activated in the emergency situation for generating torque for retracting the seat belt; and reference numeral 12 indicates a bush for transferring the torque for retracting the seat belt generated by the pretensioner 11 to the spool 4.
The lock mechanism 6 has a locking base 14 (locking member). The locking base 14 is fixed to and integrally rotatable with a first torque transferring shaft 17 of the torsion bar 7, and loosely supports a pawl 13. The torsion bar 7 has a locking gear 6a. Normally, the locking gear 6a integrally rotates with the torsion bar 7. In an emergency situation, the deceleration sensing mechanism 5 is activated to stop the locking gear 6a, so that a rotational difference is generated between the locking gear 6a and the torsion bar 7. The rotational difference causes the pawl 13 to engage an inner tooth 19 on the sidewall of the frame 2, so that the rotation of the locking base 14, i.e. the spool 4, in the seat belt withdrawal direction is stopped.
The torsion bar 7 engages the first torque transferring shaft 17 not to rotate relative to the locking base 14. The torsion bar 7 also engages a second torque transferring shaft 18 not to rotate relative to the spool 4. A circular stopper 15 is interposed between the spool 4 and a shaft 14a of the locking base 14. A female screw 15a formed on the inner circumference of the stopper 15 is screwed together with a male screw 14c formed on the shaft 14a of the locking base 14. The stopper 15 is prevented from rotating relative to an axial hole formed on the spool 4, and is movable in the axial direction of the spool 4. The rotation of the spool 4 in the seat belt withdrawal direction relative to the locking base 14 causes the stopper 15 to integrally rotate with the spool 4 and move to the right in FIG. 5.
The spring mechanism 8 constantly urges the spool 4 in the seat belt retraction direction via the bush 10, the torsion bar 7, the second torque-transferring shaft 18 of the torsion bar 7, and the bush 12. When the pretensioner 11 is activated, seat belt retraction torque generated by the pretensioner 11 is transferred to the spool 4 via the bush 12, so that the spool 4 retracts the seat belt 3 by a predetermined length.
As described above, the seat belt retractor 1 holds the seat belt 3 with the force of the spring mechanism 8 when a passenger is not wearing the seat belt 3. When the passenger withdraws the seat belt 3 at a normal speed to wear the seat belt 3, the spool 4 rotates in the seat belt withdrawal direction and the seat belt 3 is withdrawn smoothly. A tongue (not shown) is slidably attached to the seat belt 3. After the tongue is inserted and latched into a buckle fixed to the vehicle, an excess portion of the seat belt 3 is retracted on the spool 4 with the force of the spring mechanism 8. In this way, the seat belt 3 fits tightly to the passenger and the passenger does not feel too much pressure.
In an emergency situation, the pretensioner 11 transfers the generated seat belt retraction torque to the spool 4. The spool 4 retracts the seat belt 3 by a predetermined length and restrains the passenger quickly. When the vehicle quickly decelerates during the emergency situation, the deceleration sensing mechanism 5 is activated to activate the lock mechanism 6. More specifically, the activation of the deceleration sensing mechanism 5 prevents the rotation of the locking gear 6a in the seat belt withdrawal direction. Then, the pawl 13 of the lock mechanism 6 rotates and engages the inner tooth 19 of the sidewall of the frame 2. As a result, the rotation of the locking base 14 in the seat belt withdrawal direction is stopped, so that the torsion bar 7 twists and the spool 4 rotates in the seat belt withdrawal direction relative to the locking base 14. After this, the spool 4 rotates in the seat belt withdrawal direction while the torsion bar 7 twists. The twisting torque absorbs the kinetic energy of the passenger, and, consequently, the seat belt 3 generates limited load. The torsion bar 7 functions as an EA mechanism. The load of the EA mechanism (hereafter referred to as EA load) controlled by the torsion bar 7 increases first with a rotational speed of the spool 4 relative to the locking base 14, and then levels off.
When the spool 4 rotates in the seat belt withdrawal direction relative to the locking base 14, the stopper 15 moves to the right along the shaft as shown in FIG. 5. When the stopper 15 reaches an end of the male screw of the locking base 14, the stopper 15 does not move any further to the right. Accordingly, the rotation of the stopper 15 is locked, so that the stopper 15 does not rotate relative to the locking base 14. When the stopper 15 contacts a side of a flange 14b of the locking base 14, the stopper 15 is also stopped in the right axial direction. Accordingly, the spool 4 does not rotate relative to the locking base 14. More specifically, the spool 4 is locked not to rotate in the seat belt withdrawal direction, and the seat belt 3 is not withdrawn. In this way, the seat belt 3 stops the passenger moving due to inertia.
In the conventional seat belt retractor, when the seat belt is suddenly withdrawn, the locking base 14 of the lock mechanism 6 rotates in the seat belt withdrawal direction relative to the locking gear 6a. The pawl 13 of the lock mechanism 6 engages the inner tooth 19 on the sidewall of the frame 2 as described above. As a result, the rotation of the locking base 14 is locked, so that the torsion bar 7 stops the spool 4 not to rotate in the seat belt withdrawal direction. Consequently, the withdrawal of the seat belt 3 is prevented.
In the conventional seat belt retractor, only the torsion bar 7 generates the EA load for absorbing the kinetic energy of the passenger. To minimize the load applied to the passenger, a minimum and constant EA load for absorbing the kinetic energy of the passenger is selected.
As described above, the torsion bar 7 absorbs the kinetic energy of the passenger in an emergency situation. It is preferable that the kinetic energy of the passenger be absorbed as effectively and appropriately as possible. To effectively absorb the kinetic energy, various methods for providing variable EA load have been proposed.
As an example of a seat belt retractor having such an EA mechanism with variable EA load, a seat belt retractor having a second torsion bar disposed inside a cylindrical first torsion bar has been disclosed in Japanese Patent Publication (Kokai) No. 2000-16243 and Japanese Patent Publication (Kokai) No. 2000-25567. In the seat belt retractor, the first and the second torsion bars are connected at corresponding ends thereof on the same sides in the rotational direction. In an emergency situation, at first both of the torsion bars twist and deform to absorb a large amount of energy. When the first torsion bar breaks, only the second torsion bar twists to absorb the kinetic energy. In this way, the EA load changes in two steps.
As another example of the conventional seat belt retractor including the EA mechanism with variable EA load, Japanese Patent Publication (Kokai) No. 10-258702 has disclosed a seat belt retractor having a shaft disposed inside a cylindrical spool for retracting webbing and a bifacial curved EA plate with a controller interposed between the spool and the shaft. One end of the EA plate receives the rotational force of the spool in the webbing retraction direction, and the other end thereof is fixed to the shaft. In the seat belt retractor, the spool rotates in the webbing withdrawal direction relative to the shaft in an emergency situation. The rotational force of the spool in the webbing withdrawal direction is applied to the one end of the EA plate, so that the EA plate plastically deforms. As a result, the kinetic energy is absorbed and the deformation force is changed through the controller. In other words, the amount of energy absorption is changed, and the EA load is variable.
As a further example of the conventional seat belt retractor including the EA mechanism with variable EA load, Japanese Patent Publication (Kokai) No. 2000-43677 has disclosed a seat belt retractor having a torsion bar disposed inside a spool and a stopper ring disposed on a side of the spool. In the seat belt retractor, the spool rotates relative to a pawl holder in the webbing withdrawal direction during an emergency situation. As a result, the torsion bar twists, and then an engagement shoulder of the pawl holder cuts an inner circumference of the stopper ring. In this way, a large amount of the kinetic energy is absorbed. Once the inner circumference of the stopper ring is cut completely, the kinetic energy is absorbed only by the torsion bar. In this way, the EA load changes in two steps.
In the EA mechanism having two torsion bars disclosed in Japanese Patent Publication (Kokai) No. 2000-16243 and Japanese Patent Publication (Kokai) No. 2000-25567, the first torsion bar has an axial length same as that of the second torsion bar, i.e. a main torsion bar. Accordingly, the EA load depends on the axial length of the second torsion bar. For this reason, it is possible to change the EA load within a limited range, and it is difficult to set an arbitrary EA load regardless of the axial length of the second torsion bar.
The EA mechanism composed of the EA plate having the controller disclosed in Japanese Patent Publication (Kokai) No. 10-258702 has a complex shape because the EA plate is formed of a bifacial curved surface. Further, the EA mechanism has a complex structure. In addition to the complex shapes and structures of the EA plate and the EA mechanism, it is necessary to from the controller through local curing, thereby making it difficult to provide stable EA load.
In the EA mechanism made by the cutting disclosed in Japanese Patent Publication (Kokai) No. 2000-43677, it is difficult to provide constant stable EA load through the cutting of the inner circumference of the stopper ring.
In view of the problems describe above, the present invention has been made, and an object of the invention is to provide a seat belt retractor with a relatively simple structure and capable of setting a wide range of EA load with great stability.
Further objects and advantages of the invention will be apparent from the following description of the invention.